For the Hib vaccine, Haemophilus influenzae type b capsular polysaccharide is attached to a protein such as diphtheria toxoid. This attachment to the protein causes a better immune response against H. influenzae type b in infants. This Hib vaccine is a(n) __________.
A. attenuated whole-agent vaccine
B. toxoid vaccine
C. subunit vaccine
D. conjugated vaccine